1. Field of the Invention
This invention relates generally to electrical power systems that produce undesired electromagnetic fields and heat, and more particularly, to a shielding arrangement that is particularly useful in charging systems for chargeable devices, wherein the propagation of electromagnetic fields and heat is attenuated, but magnetic fields are permitted to pass with minimal eddy current losses. This invention relates generally to electrical power systems that produce undesired electromagnetic fields and heat, and more particularly, to a shielding arrangement that is particularly useful in charging systems for chargeable devices, wherein the propagation of electromagnetic fields and heat is attenuated, but magnetic fields are permitted to pass with minimal eddy current losses.
2. Description of the Related Art
Wireless charging systems transfer energy between a primary and secondary coil by creating a time variant magnetic field in the primary coil. This magnetic field also creates a similar time variant electric field or E-field. The fundamental frequency of this primary signal can be designed to lie below the AM radio band in an attempt to avoid interfering with the AM radio reception in a vehicle application.
However, it is expensive, and inefficient from the standpoint of power utilization, to eliminate the harmonics of the primary signal that spill over into the AM band and interfere with AM radio reception. There is therefore a need in the art to reduce AM band interference cause by wireless charging systems.
The prior art has sought to address issues related to magnetic interference by providing magnetic shielding around the outer volume of the primary secondary system. However, the prior art does not seem to address the particular concerns of an automotive application of wireless charging and its interference with the AM radio reception.
Another problem inherent in wireless charging is the temperature rise of the charger surface that contacts the chargeable device. Excessive temperature rise of this surface will cause the chargeable device to terminate charging in order to protect itself from overheating. The difficulty in removing the waste heat from the charging coil is that there can be no conductive loop established above the coil because of eddy current formation. Therefore, a solid electrically conductive material cannot be placed above the coil to function as a heat sink.
There is therefore in the art a need for a wireless charging arrangement that, in addition to reducing, and preferably eliminating, AM band interference, the wireless charging arrangement does not cause the charger surface to generate excessive heat.
It is, therefore, an object of this invention to provide a wireless charging arrangement for a handheld device that does not cause undue heat to be transferred to the handheld device.
It is another object of this invention to provide a system for attenuating electromagnetic energy stemming from an electrical apparatus that would cause interference in a frequency range of interest to transmission of information.
It is also an object of this invention to provide a system for attenuating electromagnetic energy that would interfere with radio transmission signals.
It is a further object of this invention to provide a system for attenuating electromagnetic energy that would interfere with radio transmission signals of a predetermined frequency range, but would permit radio signals of a different frequency range to pass through substantially without being attenuated.